A variety of implantable battery operated medical devices are available and/or under development for treating a wide range of physiological insufficiencies. Such devices uniformly require batteries which are small, light, safe, and reliable. It is additionally generally important that the batteries exhibit a high energy density and that they be amenable to implementation in a wide range of shapes and sizes to best utilize the space available in a medical device housing. Other applications in which size, safety, and reliability are desirable include aerospace and hybrid electric vehicle applications.
A significant challenge in battery design and construction is to provide an electrode assembly which can be readily manufactured and whose attributes are consistent with a battery implementation possessing the aforementioned characteristics.
The prior art reveals an abundance of electrode assembly configurations for use in batteries including configurations of stacked planar electrodes and configurations of rolled sheet electrodes. A typical stacked electrode design comprises a multiplicity of planar layers including positive electrodes (+), negative electrodes (−), and separator sheets (s) stacked in an exemplary sequence as follows: −, s, +, s, −, s, +, s, etc. Stacked electrode configurations frequently use tabs extending from the positive electrodes which are electrically interconnected to form a positive current collector. Similarly, tabs extending from the negative electrodes are electrically interconnected to form a negative current collector. The positive and negative current collectors are generally connected to first and second terminals extending externally of the battery case. In some configurations, the battery case functions as one of the external terminals.
Although known stacked electrode configurations using tabs may be suitable for use in certain applications, significant challenges are encountered when attempting to use such configurations for medical applications having small size and high energy density requirements. For example, stacked electrodes with tabs generally consume, or waste, headspace within the battery case. Thus, the energy density of a battery using conventional stacked and tabbed electrodes is constrained by the wasted headspace. Moreover, some conventional stacked designs do not lend themselves to easy fabrication and as a result manufacturing costs can be relatively high and reliability problems can be encountered.